This invention relates generally to medical diagnostic systems. In particular, the present invention relates to methods and apparatus for acquiring and processing diagnostic data sets to identify the location of the transition between different types of tissue and between tissue and blood.
Coronary artery disease (CAD) has many known causes. The early detection and treatment of significant occlusive CAD before infarction is an important goal in reducing the downstream consequences of CAD. Many variables contribute to vascular health and may prove useful in the search for early markers of at-risk individuals. For example, echocardiography has the ability to measure one of the most important of the early markers, atherosclerotic burden. Atherosclerotic burden may be measured crudely during transesophageal echocardiography of the aorta. Further, as usually performed in clinical practice, the detection of plaque is qualitative at best, making it unlikely that robust data can be derived for early detection of preclinical artherosclerosis. Far more carefully studied is high resolution B-mode ultrasound scanning of the carotid arteries with measurement of intima-medial thickness (IMT). This test has been a mainstay of epidemiologic investigations of coronary and cerebrovascular disease for decades. Excellent data document the validity of using carotid findings to predict the state of the coronary circulation, and carotid IMT both detects patients with current disease as well as accurately predicting future cardiac and cerebrovascular events. Carotid IMT measurements have been proven to provide incremental data to traditional risk prediction based on clinical data. It is the only imaging test recommended by the American Heart Association for this purpose. Ultrasound imaging allows precise measurement of the total intima and media thickness of large-and medium-size peripheral arteries like the carotid, femoral, or radial arteries. A known method to measure IMT is based on high-resolution B-mode imaging. Repeated and averaged manual measurement is relatively easy to perform, but is operator-dependent and of poor reproducibility. An accurate measurement with excellent reproducibility can be achieved only by using computer-assisted automatic methods.
However, in some instances it may be difficult to visualize the intima-media structure clearly and measure the IMT under a standard B-mode ultrasound exam. Such difficulties may be caused by technical issues, the presence of plaque buildup, or certain pathology or other disease.
IMT is defined as the distance between the kumen-intima (intima-lumen) interface and the media-adventitia (adventitia-media) interface. Such interfaces are well defined only for posterior wall where there is a clear interface between the anechoic vessel lumen and the echogenic intima, and between the hypoechoic media and the echogenic adventitia. Even when the anterior IMT is well visualized, its measurement remains gain-dependent and unreliable. The proximal IMT measurements are reliable and reproducible only when done on the contrast enhanced images